IN HUMAN PHYSIOLOGY. 199 



41. How often do we wink ? 

 Five or six times a minute. 



42. Why is the interior of a telescope or microscope often 

 painted black 1 



To absorb the scattered rays of light which would 

 confuse the vision. For the same reason, the posterior 

 'surface of the iris, the ciliary processes and the choroid 

 are covered with a layer of dark pigment. 



43 . What is " the apple of the eye ?" 

 The pupil. 



44. What form of glasses do old people require ? 



(See Question 22.) 



45. Should we ever wash our ears with cold water? 

 Rarely, if ever, lest we chill this sensitive organ. 



46. What is the object of the winding passages in the 

 nose? 



To furnish additional surface on which to expand the 

 olfactory nerve. 



47. Can a smoker tell in the dark, whether or not his 

 cigar is lighted? 



Sight often seems to be essential to perfect what we 

 call a sensation of taste. 



48. Will a nerve re-unite after it has been cut ? 

 Nerve-fibre seems to re-unite as readily as muscle-fibre. 



